Air ducts are used to distribute air through out a building, or to exhaust air outside of a building. The most common are: sheet metal air duct, fiberglass lined air duct, fiberboard air duct, flexible air duct, Polyisocyanurate Foam Panel air duct (PIR). An air duct system is often called ductwork. Planning, sizing, optimizing, detailing, and finding the pressure losses through a duct system.